In well drilling operations, joints of drill pipe are generally connected one after the other to the upper end of the drill string. Drill pipe joints are typically stored near the rig platform, from where they are retrieved, one by one, and placed in a vertical holding tube known as a “mousehole.” The mousehole holds the joint in a vertical orientation, in preparation for connection for the drill string. The mousehole is typically positioned underneath the drill floor and has an opening in the drill floor, near region of the drill floor where drill pipe connection takes place. It is also well known to use a so-called “powered mousehole”, which in fact is a mousehole with an elevating bottom, allowing for adjustment of the mousehole length (depth).
The state of the art includes U.S. Pat. No. 5,468,121, which discloses a mousehole installed underneath rig floor. The mousehole comprises a longitudinally oriented sleeve depending from the rig floor. The sleeve includes an open top end more or less flush with the rig floor, a closed bottom end, and a wall. Arranged at the bottom end of the mousehole is an expandable (inflatable) bladder which may be used for elevating the pipe joint in the mousehole. The mousehole disclosed in U.S. Pat. No. 5,468,121 also comprises a carriage disposed adjacent to the bottom end of the mousehole and which is operatively engaged by a hoist. The hoist includes a cable guided in a groove of a sheave mounted in the carriage. The cable is secured at one end to an outer surface of the sleeve by means such as a pad eye and looped through parallel slits formed longitudinally on opposite sides in the sleeve for engagement with the sheave. The other end of the cable is then attached to a reel of the hoist in the rig floor. When it is desired to elevate the pipe joint for raising its upper end above the rig floor, the hoist is activated to draw in or shorten the cable and, in turn, elevate the carriage within the mousehole.
A key factor in the design of mouseholes is of course the length of the tubular to be handled; this dictates the overall length of the mousehole. Mousehole lengths of 40 feet (12 meters) to 75 feet (23 meters) are common. The mousehole extends though the drill floor and into the space underneath the drill floor, above the cellar deck.
On a drilling rig, it is of utmost importance to have access to the entire cellar deck area. Of particular importance is the ability to move the overhead cranes. Such overhead are suspended from underneath the drill floor structure, above the cellar deck. State-of-the-art mouseholes, which are suspended from the drill floor deck, will interfere with the operation of crane(s) in the cellar deck area. Therefore, to ensure unimpeded crane movements above the cellar deck, the only solution is to disconnect all utilities, connect any external lifting device at the drill floor level, and pull them out. This is a troublesome, time consuming and in many cases a somewhat risky operation.
The present applicant has devised and embodied this invention in order to overcome these shortcomings and to obtain further advantages.